Recently, integration technologies of semiconductor devices are remarkably developed, enabling to design multi-functional microcomputer chips without difficulties. As an example of them, there is realized a bi-functional microcomputer chip equipped with additional patterns for in-circuit emulation, in order to economize times and costs for program developing, wherein the additional patterns are to be inactivated when the microcomputer chip is served for its original use. For the purpose, there is provided a bonding pat on the microcomputer chip of this kind, connected to an input circuit for selecting an operation mode of the microcomputer and to be bonded in a manufacturing process to a ground GND or a power supply VDD for determining the operation mode according to actual use.
As it is impractical to prepare bonding pads for the ground GND and the power supply VDD right and left of the bonding pad for mode setting, the input circuit is generally designed to control the operation mode corresponding to whether the concerning bonding pad is bonded to the ground GND, for example, or left open un-bonded.
However, when the bonding pad is merely left open, a through current flows from the power supply VDD to the ground GND through an nMOS transistor and a pMOS transistor consisting in the input stage of the input circuit with their gates connected to the bonding pad left at high impedance, dissipating a power consumption. So, some countermeasures are devised for preventing the through current, by providing a pull-up resistor in the input stage, for example.
According to an invention described in the U.S. Pat. No. 5,764,075, logical status of a mode signal is latched in response to a RES signal and controls the status (on or off) of a pull-up resistor. However, the conventional circuit, according to the U.S. Pat. No. 5,764,075, EMS (Electromagnetic Susceptibility) resistance is not excellent enough. In other words, when an external noise is applied to the circuit, malfunction would occur.